This application claims the priorities of German application 100 54 332.4, filed Nov. 2, 2000, and German application 101 51 288.0, filed Oct. 22, 2001, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to a structural antenna for a flight aggregate or aircraft having an approximately omnidirectional radiation characteristic. The structural antenna is arranged as a conductive element on a non-conductive layer which forms a base layer of a surface of an aerodynamically effective area of the flight aggregate or aircraft, with the radiating element arranged around a folding edge of the aerodynamically effective area of the flight aggregate or aircraft.
Antennas which are to be used on flight aggregates or aircraft are subjected to a number of demands. If possible, the contour of a flight aggregate or aircraft should not be influenced to such an extent that aerodynamic relationships, and thus flying characteristics, change significantly. The arrangement and the fastening of an antenna should be in accordance with the mechanical construction of the structural parts, and the mechanical stability of the structure must not be impaired. If possible, a radar backscattering cross-section should be changed only slightly.
Because antenna installation sites in flight aggregates or aircraft are very limited, it is increasingly common to install antennas in wings, tail units or pertaining control flaps. The use of antennas in these very narrowly constructed elements is problematic because the radiation characteristics in edge directions are limited considerably, since the apertures are small in these directions.
U.S. Pat. No. 5,191,351 describes a number of folded broadband antennas with symmetrical radiation characteristics. The suggested logarithmic-periodic antennas are basically suited for installation on wing edges, and antenna diagrams of these antennas correspond to the desired demands. Antenna feeding takes place at folding edges, and construction-caused limitations occur. In modern aircraft, the leading edges of wings and tail units consist of sharp, continuous metal edges in order to control stability, meet demands for low radar perceptibility, and ensure sufficient lightening protection for the antennas by low-impedance galvanic connections to the structures. The antennas described in the above-mentioned document cannot meet these requirements.
German Patent Document DE 22 12 647 B2 describes a notch antenna suitable for mounting in aerodynamically effective areas. A problem with this antenna is that the position of the feeding point in the direct proximity of the folding edge permits feeding only for larger angles of partial surfaces of the antenna.
Another variant of an antenna suitable for aerodynamically effective areas is disclosed by U.S. Pat. No. 3,039,095. In this case, the effective area may have sharp edges. Because the antenna elements are arranged on the lateral surfaces of the aerodynamically effective area, losses occur during radiation in the direction of the edges.
It is therefore an object of the invention to provide an antenna construction with an approximately omnidirectional characteristic which is suitable for installation at sharp-edged wing, tail unit, and control surface edges.
According to the invention, this object is achieved by constructing a structural antenna as a plane antenna and integrating the antenna in the surface of an aerodynamically effective area. In the range of the structural antenna, the aerodynamically effective area is formed by the dielectrically effective material of a non-conductive layer. The conductive area of the structural antenna is completely or at least partially surrounded by an area of the non-conductive layer which preferably has the shape of a strip. The structural antenna is fed in the area of the conductive area facing away from the folding edge, so that the current direction extends perpendicular to the folding edge and the characteristic impedance at the folding edge is much lower than in the range of the ends of the structural antenna which are away from the edge. Advantageous features are reflected in the claims.
A structural antenna according to the invention has a number of advantages over the prior art. Feeding does not take place at the folded edge; instead, feeding takes place away from the edge, in an area of the wing or the tail unit, in which, because of an increasing thickness of the structure, antenna installation and connection are facilitated. The possibility of a conductive connection between a structural antenna and a folding edge connected with the structure is a significant advantage in terms of protection against lightening and while manufacturing aircraft which, for reasons of stability, must be equipped with a metallic sharp edge. The sharp edge provides favorable stealth characteristics because a radar backscattering cross-section is impaired only slightly. Furthermore, an improvement can be achieved in this respect by setting edges of the structural antenna defining metallically conductive areas diagonally to the direction of the main threat, which corresponds to the flight direction, and by selecting the distances between the structural antenna and the conductive surface layer of the aerodynamically effective area so that they are very small.
Several embodiments of an antenna structure according to the invention are illustrated in the drawings in schematically simplified manners and will be described.